/**
 * This file is part of mycollab-jackrabbit.
 *
 * mycollab-jackrabbit is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * mycollab-jackrabbit is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with mycollab-jackrabbit.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.springframework.extensions.jcr.util;

import java.io.Serializable;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;

import org.springframework.util.Assert;

/**
 * A simple decorator for a Map, encapsulating the workflow for caching
 * expensive values in a target Map. Supports caching weak or strong keys.
 *
 * <p>This class is an abstract template. Caching Map implementations
 * should subclass and override the <code>create(key)</code> method which
 * encapsulates expensive creation of a new object.
 * 
 * @author Keith Donald
 * @author Juergen Hoeller
 * @since 1.2.2
 */
public abstract class CachingMapDecorator<K, V> implements Map<K, V>, Serializable {

    private static Object NULL_VALUE = new Object();


    private final Map<K, Object> targetMap;

    private final boolean synchronize;

    private final boolean weak;


    /**
     * Create a CachingMapDecorator with strong keys,
     * using an underlying synchronized Map.
     */
    public CachingMapDecorator() {
        this(false);
    }

    /**
     * Create a CachingMapDecorator,
     * using an underlying synchronized Map.
     * @param weak whether to use weak references for keys and values
     */
    public CachingMapDecorator(boolean weak) {
        Map<K, Object> internalMap = (weak ? new WeakHashMap<K, Object>() : new HashMap<K, Object>());
        this.targetMap = Collections.synchronizedMap(internalMap);
        this.synchronize = true;
        this.weak = weak;
    }

    /**
     * Create a CachingMapDecorator with initial size,
     * using an underlying synchronized Map.
     * @param weak whether to use weak references for keys and values
     * @param size the initial cache size
     */
    public CachingMapDecorator(boolean weak, int size) {
        Map<K, Object> internalMap = weak ? new WeakHashMap<K, Object> (size) : new HashMap<K, Object>(size);
        this.targetMap = Collections.synchronizedMap(internalMap);
        this.synchronize = true;
        this.weak = weak;
    }

    /**
     * Create a CachingMapDecorator for the given Map.
     * <p>The passed-in Map won't get synchronized explicitly,
     * so make sure to pass in a properly synchronized Map, if desired.
     * @param targetMap the Map to decorate
     */
    public CachingMapDecorator(Map<K, V> targetMap) {
        this(targetMap, false, false);
    }

    /**
     * Create a CachingMapDecorator for the given Map.
     * <p>The passed-in Map won't get synchronized explicitly unless
     * you specify "synchronize" as "true".
     * @param targetMap the Map to decorate
     * @param synchronize whether to synchronize on the given Map
     * @param weak whether to use weak references for values
     */
    @SuppressWarnings("unchecked")
    public CachingMapDecorator(Map<K, V> targetMap, boolean synchronize, boolean weak) {
        Assert.notNull(targetMap, "'targetMap' must not be null");
        this.targetMap = (Map<K, Object>) (synchronize ? Collections.synchronizedMap(targetMap) : targetMap);
        this.synchronize = synchronize;
        this.weak = weak;
    }


    public int size() {
        return this.targetMap.size();
    }

    public boolean isEmpty() {
        return this.targetMap.isEmpty();
    }

    public boolean containsKey(Object key) {
        return this.targetMap.containsKey(key);
    }

    public boolean containsValue(Object value) {
        Object valueToCheck = (value != null ? value : NULL_VALUE);
        if (this.synchronize) {
            synchronized (this.targetMap) {
                return containsValueOrReference(valueToCheck);
            }
        }
        else {
            return containsValueOrReference(valueToCheck);
        }
    }

    private boolean containsValueOrReference(Object value) {
        if (this.targetMap.containsValue(value)) {
            return true;
        }
        for (Object mapVal : this.targetMap.values()) {
            if (mapVal instanceof Reference && value.equals(((Reference) mapVal).get())) {
                return true;
            }
        }
        return false;
    }

    public V remove(Object key) {
        return unwrapReturnValue(this.targetMap.remove(key));
    }

    @SuppressWarnings("unchecked")
    private V unwrapReturnValue(Object value) {
        Object returnValue = value;
        if (returnValue instanceof Reference) {
            returnValue = ((Reference) returnValue).get();
        }
        return (returnValue == NULL_VALUE ? null : (V) returnValue);
    }

    public void putAll(Map<? extends K, ? extends V> map) {
        this.targetMap.putAll(map);
    }

    public void clear() {
        this.targetMap.clear();
    }

    public Set<K> keySet() {
        if (this.synchronize) {
            synchronized (this.targetMap) {
                return new LinkedHashSet<K>(this.targetMap.keySet());
            }
        }
        else {
            return new LinkedHashSet<K>(this.targetMap.keySet());
        }
    }

    public Collection<V> values() {
        if (this.synchronize) {
            synchronized (this.targetMap) {
                return valuesCopy();
            }
        }
        else {
            return valuesCopy();
        }
    }

    @SuppressWarnings("unchecked")
    private Collection<V> valuesCopy() {
        LinkedList<V> values = new LinkedList<V>();
        for (Iterator<Object> it = this.targetMap.values().iterator(); it.hasNext();) {
            Object value = it.next();
            if (value instanceof Reference) {
                value = ((Reference) value).get();
                if (value == null) {
                    it.remove();
                    continue;
                }
            }
            values.add(value == NULL_VALUE ? null : (V) value);
        }
        return values;
    }

    public Set<Map.Entry<K, V>> entrySet() {
        if (this.synchronize) {
            synchronized (this.targetMap) {
                return entryCopy();
            }
        }
        else {
            return entryCopy();
        }
    }

    @SuppressWarnings("unchecked")
    private Set<Map.Entry<K, V>> entryCopy() {
        Map<K,V> entries = new LinkedHashMap<K, V>();
        for (Iterator<Entry<K, Object>> it = this.targetMap.entrySet().iterator(); it.hasNext();) {
            Entry<K, Object> entry = it.next();
            Object value = entry.getValue();
            if (value instanceof Reference) {
                value = ((Reference) value).get();
                if (value == null) {
                    it.remove();
                    continue;
                }
            }
            entries.put(entry.getKey(), value == NULL_VALUE ? null : (V) value);
        }
        return entries.entrySet();
    }


    /**
     * Put an object into the cache, possibly wrapping it with a weak
     * reference.
     * @see #useWeakValue(Object, Object)
     */
    public V put(K key, V value) {
        Object newValue = value;
        if (value == null) {
            newValue = NULL_VALUE;
        }
        else if (useWeakValue(key, value)) {
            newValue = new WeakReference<Object>(newValue);
        }
        return unwrapReturnValue(this.targetMap.put(key, newValue));
    }

    /**
     * Decide whether to use a weak reference for the value of
     * the given key-value pair.
     * @param key the candidate key
     * @param value the candidate value
     * @return <code>true</code> in order to use a weak reference;
     * <code>false</code> otherwise.
     */
    protected boolean useWeakValue(K key, V value) {
        return this.weak;
    }

    /**
     * Get value for key.
     * Creates and caches value if it doesn't already exist in the cache.
     * <p>This implementation is <i>not</i> synchronized: This is highly
     * concurrent but does not guarantee unique instances in the cache,
     * as multiple values for the same key could get created in parallel.
     * Consider overriding this method to synchronize it, if desired.
     * @see #create(Object)
     */
    @SuppressWarnings("unchecked")
    public V get(Object key) {
        Object value = this.targetMap.get(key);
        if (value instanceof Reference) {
            value = ((Reference) value).get();
        }
        if (value == null) {
            V newValue = create((K) key);
            put((K) key, newValue);
            return newValue;
        }
        return (value == NULL_VALUE ? null : (V) value);
    }

    /**
     * Create a value to cache for the given key.
     * Called by <code>get</code> if there is no value cached already.
     * @param key the cache key
     * @see #get(Object)
     */
    protected abstract V create(K key);


    @Override
    public String toString() {
        return "CachingMapDecorator [" + getClass().getName() + "]:" + this.targetMap;
    }

}

